Attempts to decrease the volume of apparatus for use with instant type film, eg., cameras and camera backs, have been successful, in part, by providing the film units with a chemical opacification system for preventing further exposure of the film unit's emulsion or photosensitive layer by the ambient light during the formation of a visible image, thus obviating the need for a lighttight imbibition chamber in the apparatus. However, providing such apparatus with a lighttight imbibition chamber may provide one with benefits which offset, in part, any disadvantage caused by the space which it takes up. For example, removal of the opacification material, e.g., opacifying dyes, from the processing liquid of an instant type film unit would reduce the cost of the processing liquid. Further, the layer of processing liquid which is to be spread between the image receiving layer and the photosensitive layer could thereby be thinner thus improving resolution of the image and reducing the time required to produce a visible image.
The overall volume of instant type cameras having lighttight imbibition chambers may be minimized by moving the exposed film unit away from its cassette and then reversing its movement and directing it to an imbibition chamber located substantially under the cassette. A typical example of such a camera is described in U.S. Pat. No. 3,537,370. It includes a bulky pivotable container external of the camera housing to receive the exposed film unit after its exposure and just prior to its processing and this adds to the bulk of the camera.
A more recent development for storing film units behind the film cassette within the camera housing is illustrated in U.S. Pat. No. 4,664,497. It includes a lighttight imbibtion chamber in which an exposed film unit is adapted to remain until its latent image has been substantially transformed into a viewable image. The apparatus includes a housing enclosing a film chamber having structure for locating and supporting a film assemblage in position for the sequential exposure of a plurality of film units located therein. Located rearwardly or below the film assemblage supporting structure is a chamber which is adapted to receive an exposed film unit, subsequent to a processing liquid being spread across a layer thereof, and maintain it in a lighttight environment until the processing liquid has sufficiently imbibed the film unit for a period of time after which ambient light will not adversely affect the emerging visible image. The apparatus includes a battery operated motor mounted adjacent one end of the film assemblage supporting structure and means for advancing an exposed film unit from the assemblage's film cassette, around the motor and then to the lighttight imbibition chamber. The aforementioned advancing means includes a cantilevered member having a free end which is adapted to move an uppermost film unit from the film cassette; laterally spaced pairs of superposed friction wheels which are adapted to engage the lateral sides of the exposed film unit and continue its movement away from the film cassette and around the motor and toward a pair of cylindrically configured superposed rollers; the superposed rollers; and a second cantilevered member for advancing the exposed film unit into the lighttight imbibition chamber. The rollers are adapted to rupture a container of processing liquid carried on a leading end of the advancing film unit and spread its contents across a layer thereof to initiate the formation of a visible image therein by a diffusion process. As the exposed film unit leaves the bite of the rollers, its trailing end is located in a position to be engaged by the second cantilevered member for subsequent movement into the imbibition chamber. The apparatus further includes a loading door through which a film assemblage may be located on the aforementioned supporting structure. The loading door, which comprises one of the walls of the imbibition chamber, has a window therein through which the visible image in a film unit located within the imbibition chamber may be viewed without opening the loading door. Such window is ordinarily rendered lighttight by a blind which is movable from its operative position covering the window, to an inoperative position wherein the film unit within the chamber may be viewed. The blind is maintained in the operative position by a latch until the formation of a visible image within the last exposed unit to enter the imbibition chamber has been substantially formed. After the formation of the visible image, a timing circuit energizes a solenoid to move the latch to a position wherein the blind may be moved to its inoperative position. The imbibition chamber is also provided with a light sealed opening through which all of the film units located within the imbibition chamber may be moved as a unit to the exterior of the photographic apparatus. Suitable means, such as a manually actuatable slide, is provided for such purpose.
A problem with apparatus of the type described in the aforementioned '497 patent to B. Johnson et al. is that the momentum of the film unit as it exits from the bite of the spread rollers may not be sufficient to completely move the trailing end of the film unit from full and complete engagement with the spread rollers. Thus, when this happens, the trailing end of the film unit does not drop into a position wherein it may be engaged by the second cantilevered member for subsequent movement into the lighttight imbibition chamber.